1. Technical Field
Embodiments of the present invention relate to a recording device and a recording system for recording various data using a recording disk, such as a magnetic disk or an optical disk, and transferring the recorded data to another recording device to enable backup, and particularly to a technique for high-speed backup of data.
2. Description of the Related Art
Recording devices and recording systems for recording various data using recording disks, such as magnetic disks or optical disks, are broadly used. As recording devices which enable backup of data to another recording device, for example, many relatively large-scale recording devices are employed for business use which enable backup to another recording device through a leased or public telecommunication line. As for personal computers, it is known that data on an integrated hard disk device can be backed up to another integrated hard disk device through an internal signal line or can be backed up to an external hard disk device through a connection cable. The purpose of backup is, for example, to prevent loss of data due to failures in the recording devices, natural disasters such as earthquakes, or other accidents. To simplify the explanation, all of the above-described telecommunication lines, signal lines and connection cables will be referred to as a signal line in the following description.
FIG. 12 is a block diagram showing the schematic structure of conventional recording devices and a recording system which enable backup.
In FIG. 12, reference numerals 1 and 2 each represent a recording device using a recording disk. Reference numeral 3 represents an administration device for administering the recording devices 1 and 2, including the backup of data. Reference numeral 5 represents a signal line directly connecting the recording devices 1 and 2. Reference numeral 6 represents a signal line connecting the recording device 1 with the administration device 3. Reference numeral 7 represents a signal line connecting the recording device 2 with the administration device 3. The recording devices 1 and 2 are indirectly connected with each other by the signal lines 6 and 7 through the administration device 3. A typical recording system may have one of the paths of the signal line 5 and the signal lines 6 and 7, or may have both of these paths.
The illustrated recording devices 1 and 2 have the same structure. In the recording device 1, a data storage unit 12 for storing various data using a recording disk, a data allocation storage unit 13 for storing data allocation indicating where and what data are recorded on the recording disk, and a control unit 11 for controlling transmission/reception of data to/from outside through the signal line 5 or 6, writing of data received from outside, recording of written data allocation information to data allocation storage unit 13 and reading of data from the recording disk on the basis of data allocation storage unit 13 are provided. Also, recording device 2 is provided with similar units, i.e., a data storage unit 22, a data allocation storage trait 23 and a control unit 21.
In the case of reading data from data storage unit 12 of recording device 1 and writing the data to data storage unit 22 of recording device 2 for backup, for example, data is sent directly from the recording device 1 to recording device 2 through the signal line 5, or data is sent indirectly from recording device 1 to recording device 2 through the signal line 6, administration device 3 and signal line 7. When the path of signal line 5 and the path using signal lines 6 and 7 are both provided, the burden of the operation for backup of data from recording device 1 to recording device 2 in the administration device 3 can be reduced by directly sending the data through signal line 5.
Generally, in a recording device using a recording disk, when erasing recorded data, only data allocation information, such as addresses of start and end storage areas of data stored in the data allocation storage unit, is erased, without erasing the actual data stored in the data storage unit. For example, in recording device 1, data written in data storage unit 12 is not erased and only data allocation information in data allocation storage unit 13 is erased. This is because when writing new data, a storage area having no data allocation information in data storage unit 12 may be overwritten with the new data, and it is not necessary to take time to erase data written in data storage unit 12.
FIG. 13 shows a simplified example of data storage unit 12 and data allocation storage unit 13 in the situation of erasing data in the recording device 1.
The left side of FIG. 13 shows data storage unit 12 and data allocation storage unit 13 before erasing data. The right side of FIG. 13 shows data storage unit 12 and data allocation storage unit 13 after erasing data.
Data storage unit 12 is a recording disk having, recording tracks TR0 to TR7. Each track is divided into seven sectors, which are smallest recording units (storage areas). Therefore, there are fifty six sectors SC0 to SC55 for the eight recording tracks TR0 to TR7.
In data allocation storage unit 13, allocation information of seven data D1 to D7 is recorded. For example, data D1 is recorded in sectors SC0 to SC5 of track TR0, and data D5 is recorded in discontinuous storage areas in the recording disk, i.e., sector SC19 of track TR2 to sector SC24 of track TR3 and sectors SC43 to SC47 of track TR6.
In recording device 1 of FIG. 13, for example, when data D5 is erased from the left side of FIG. 13, which shows the state-before erasing data, only allocation information of data D5 is erased from data allocation storage unit 13 and data storage unit 12 remains unchanged, as seen from the right side of FIG. 13, which shows the state after erasing data. On the right side of FIG. 13, which shows the state after erasing data, the data recorded in sector SC19 of track TR2 to sector SC24 of track TR3 and sectors S43 to SC47 of track TR6 remains as it is.
In the case of backing up, to recording device 2 of FIG. 12, the data in recording device 1 in the state after erasing data shown on the right side of FIG. 13, the contents of data D5 recorded in sector SC19 of track TR2 to sector SC24 of track TR3 and sectors SC43 to SC47 of track TR6 in data storage unit 12 are read out from recording device 1 and written to recording device 2 as they are, though the data need not be backed up.
FIG. 14 shows the states of data allocation storage units and data storage units on both the reading side and the writing side in the case of carrying out backup between the conventional recording devices.
The left side of FIG. 14 shows data storage unit 12 and data allocation storage unit 13 of recording device 1 as the data reading side. The right side of FIG. 14 shows data storage unit 22 and data allocation storage unit 23 of recording device 2 as the data writing side.
In FIG. 14, since allocation information of data D5 is erased in data allocation storage units 13 and 23, sector SC19 of track TR2 to sector SC24 of track TR3 and sectors SC43 to SC 47 of track TR6, where data D5 is stored, in data storage unit 12 on the reading side shown on the left side of FIG. 14, are not used and have invalid data. In short, the data in sectors SC19 to SC24 and sectors SC43 to SC47 in data storage unit 12 is not erased and remains as data even if its allocation information is erased, which is data of invalid areas.
In data storage unit 22 on the writing side shown on the right side of FIG. 14, since all the data in data storage unit 12 is written as it is, the data in sectors SC19 to SC24 and sectors SC43 to SC47, which are invalid areas, is also written.
However, recording devices with larger capacity as desired because of the spread of multimedia and networking in recent years and, therefore, recording disks have had larger capacity. In this situation, for example, the quantity of invalid data, such as erased data in a recording disk used for a long time, may be increased to a level that is not negligible. Therefore, at the time of backup, the time required for reading and writing the erased data is increased and a very long time is necessary for backup. Since, during backup, the capability of the recording device may be limited or the recording device may not be used, the increase in backup time raises a problem.